The invention relates to a process for the production of a low-fibrillation moulded body containing polytetrafluorethylene, low-fibrillation moulded bodies, which can be obtained as a result of the process in accordance with the invention and the use of these as dental floss.
Polytetrafluorethylene (PTFE) is a prized material due to its thermal stability and chemical inertness. Monoaxially stretched films made from sintered PTFE are known from AT-B 370.673, the strength of which has values of between 50 N/mm.sup.2 and 140 N/mm.sup.2 in the stretching direction. Said films are produced when PTFE powder is first of all pressed to a cylindrical moulded body. The moulded body is then sintered, whereupon films are peeled off, heated to temperatures of at least 327 C and stretched.
GB-A 2 025 835 describes the production of porous PTFE moulded bodies in accordance with the paste extrusion process whereby a paste-like mass, which basically comprises PTFE powder and a lubricant (hydrocarbon), is pressed through dies whereby the lubricant is removed by drying. The moulded body is then heated to above the crystallite melting point of the PTFE (327.degree. C.) and stretched during heating.
EP-A 0 391 887 describes a process for the production of a monoxially stretched moulded body of PTFE, in which a paste-like PTFE mass is continuously processed to a moulded body which is led over a number of rollers or cylinders, heated and stretched, the moulded body being heated to a temperature between 327.degree. C. and 450.degree. C. before applying the stretching and sintered. This process allows the production of a monoaxially stretched moulded bodies of PTFE with tenacity values in the stretching direction of at least 22 cN/tex (500 N/mm.sup.2).
Furthermore, it is known that moulded bodies of PTFE can be made available with different filling substances. Moulded bodies of this kind containing filling substances are for example known from AT-B399 882 and contain talc and/or mica and/or a high temperature resistant polyimide of between 20 and 30 wt. % as a filling material. The PTFE moulded bodies described in AT-B 399 882 containing filling materials are for example suitable for use as dental floss.
Dental flosses of PTFE tapes are moreover described in EP-A 0 335 466, U.S. Pat. No. 5,209,251 and U.S. Pat. No. 5,220,932. The PTFE-tapes can have different densities and can be in a folded or unfolded state.
Compared to conventional dental flosses e.g. of polyamide, the PTFE material is softer which means greater suppleness and softness which results in a lower risk of hurting the flesh of the gums when in use.
Since they are in a stretched or expanded state, PTFE tapes tend to fibrillate which means that individual fibres split. This leads to problems either when unreeling the dental floss from the dental floss dispenser respectively when the dental floss splits when in use leaving traces of dental floss between the teeth.
In PCT-WO 95/34252 a dental floss is suggested from an unfolded expanded PTFE fibre which has a regular thickness and width overall whereby the parallel placed edges of the dental floss are resistant to fibrillation. In this respect a thicker PTFE sheet in comparison to state of the art is cut into equally thick and broad strands. The strands are rolled up without prior folding.